The present invention relates generally to root canal filling, retrofilling, and perforation materials. More particularly, the present invention relates to a sealer paste and core material for root canal filling, retrofilling, and perforation.
Endodontic therapy (also identified as root canal therapy) involves the removal of all tooth pulp space contents, potentially infected and diseased tissue and their by-products from the root system of a tooth. Once these materials are removed from the root system, the root canal is shaped to facilitate filling. The root canal is then filled.
While there are many techniques for root canal filling, the most widely used technique uses a combination of gutta percha cones and a zinc oxide-eugenol based sealing material. This technique has also been used with retrograde root canal filings following apicoectomy (also referred to as retrofillings) and for the repair of tooth root perforations.
A critical factor in the long-term success of endodontic therapy involves eliminating leakage around and through a root canal filling, a retrofilling, or a perforation repair. Intimate adaptation of the filling material to the root canal typically plays an important role in eliminating leakage. However, attaining intimate adaptation is difficult.
Johnson, U.S. Pat. No. 5,372,759, and Fujisawa et al., U.S. Pat. No. 4,931,096, describe using warm vertical condensation of gutta percha to reduce leakage around and through the root canal filling. Takubo, U.S. Pat. No. 4,657,592, describes using a filling material that remains semi-solid at body temperature but which is softened by heating during the filling process.
One variation in endodontic sealers is to replace the aromatic compound eugenol with carboxylic acids that react with zinc oxide. For example, Molnar, U.S. Pat. No. 3,028,247 describes using caprylic acid (also known as octanoic acid) and lauric acid (also known as dodecanoic acid) as reactants.
Dainippon Toryo KK, Japanese Patent No. 3,027,309, describes using a sealer that adheres to the gutta percha cone to reduce leakage through the root canal filling material. However, potential problems that are associated with leakage at the margins with dentin are still experienced.
Kahn, U.S. Pat. No. 4,526,544, discusses using cyanoacrylate adhesives to bond both to dentin and gutta percha. A drawback of the cyanoacrylate adhesives is that they chemically break down in biological environments, such as are present in the mouth.
In an article entitled, A New Dental Cement, 125 British Dental J. 381 (1968), Smith describes mixing an aqueous solution of poly(acrylic acid) with zinc oxide. This adhesive was identified as zinc polycarboxylate or zinc polyacrylate cement.
It has also been described to use poly(acrylic acid) or a closely related co-polymer with aluminosilicate glass powders to produce translucent dental cement. Wilson et al., 132 British Dental J. 133 (1972). Wilson et al. indicates that the polymer is either in aqueous solution or a dry powder, which is mixed with water.
Combe et al., U.S. Pat. No. 5,141,560, discloses a calcium hydroxide pulp-capping material that is prepared from a non-aqueous cement that contains dry poly(acrylic acid). Adhesion to dentin was achieved through moisture from the tooth structure being absorbed into the cement. This absorption results in partial dissolution of the polymer.
The prior art root canal obturation materials generally fall into three general groups. The first group is gutta percha cone with zinc oxide-euaenol paste. The second group is glass ionomer. The third group is calcium hydroxide.
These root canal filing materials each typically exhibit good dimensional stability, are radiopaque, and do not provoke an immune response. These materials are also bacteriostatic, sterilizable, non-mutagenic, and non-carcinogenic.
Several drawbacks of the gutta percha cone and zinc oxide-eugenol paste technique are that these materials do not form a hermetic seal. The gutta percha/zinc oxide-eugenol material also tends to irritate periapical tissues and is porous to moisture. Additionally, the gutta percha/zinc oxide-eugenol material is degraded by long-term exposure to tissue fluids that are typically present in the mouth.
It is difficult to form a hermetic seal of the root canal using glass ionomer. Glass ionomer is not impervious to moisture and is not non-porous. Another drawback of glass ionomer is that it is difficult to remove the glass ionomer when it is necessary to retreat the root canal. Yet another drawback of glass ionomer is that glass ionomer irritates periapical tissue.
The calcium hydroxide technique has a very limited working time before setting. It is also difficult to form a hermetic seal with the calcium hydroxide filling material. The calcium hydroxide filling material is degraded by long-term exposure to tissue fluids that are typically present in the mouth. This material is also not impervious to moisture.